Low frequency oscillator



06%. 12, 1.948. E R SHENK ET AL l 2,451,245

Low FREQUENCY oscILLAToR Filed March 23, 1944 E OUTPUT f1: 7 2? I as llllll IN VEN TOR;

Patented Oct. 12, 1948 2,451,245;A LOW FREQUENCY 01SCIL'IJlYOR` Eugene- R.

Shenk, Brooklyn,-b afndg, Alfred Kahn, Y

Queens Village, N; Y., assignornsvtojltadio .Cor-

. poration .of America, a corpprationiof.Delaware-1 Application March 2K3, 1944;',V SerialJN'o. 527,7564

This invention relates to .low frequencyoscillation generators and particularly to a circuit arrangement forstabilizingthe frequency ofoscillat-ions generated by amechanical vibrator.

Azprimary object of the present invention isto provide a source of.oscillations of constantA frequency and Vconstant amplitude.

Another object is to provide such a source which is particularly adapted for use in the audio frequency range below ten thousandcycles.

A further object is to `provide a system for generating oscillations of constant frequency and constant amplitude which is compact and substantially unaiected `by temperature changes.

Aiurther object is to provide aV low frequency electrical lsource ofpconstantfA frequency andi constantamplitude of `output Whichmaybe operated from the standard power supplysystemsregard-fv less .of theV usual fluctuations in :voltage .encountered in suchasystem.

Astl further obj ectofour invention is to .provide a low frequencyl oscillation generator with means including limiters whereby the drivingpotentials .applied for. vibrating a tuning forkshall be maintained substantially constant.

Heretoforetuning forlss have beenoperatedjn circuits `which feda sinefwave into ,the-drive. coil. This requiresV Class A operationof all circuits betweenthe pick-up and drive coilsof theqfork.

Replacing tubes is likelyto; alter, to some extent, r thegain in this circuit. As a result, more or less. drive will besuppliedto the fork and itsamplif.

tude of oscillations increased or decreased accord. ingly. Besides the change'inl output voltage resulting from lthe new'vvalue of drive, the frequency of the forkoscillationswill befaltered somewhat.

As a means of-'overcoming-these disadvantages, various limiters and pulse drive circuits have been developed. A- feature of our nventionresides in the means relatingto the pulse drive, circuit,

Our. invention will now be,descljibel;4 in morebe Whatever is desired'. Onel terminahofeach-*Of the coils 2 andgi is;grounded -and preferably the.

tuning forkuitseli-` is.grounded. Capacitor 4 in combinationV withV1 the .inductance oi-4 coll 3 v. forms.

ata-nk circuitinwhich A. @potentials aregene erated.` These potentialseare applied to theconf. trolgrid-in a trioledischarge tubeiwhichoperf. ates as anamplifier. Thecathode. of tube Slis.

2 connected to ground through azcathode resistor 6.

The output circuitof` tube Sfincludes acapacitor. 'l-'andaapotentiometer 8 on which is atap 9 for taking off` output potentials to beapplied tothe controLgridfof 'anamplier tube. Ill.' Operating potential for.the..tube 5:1 as well Las. for other dis'-y cliarge-tubesl.' II; and I2,v maybe derivedfrom miylsuitable direct. current` source .Y (noti shown) the'. positive. terminalA of which is merely indiek cated asi, +B. The negative terminal of' this source isftobe. considered grounded. Dtschargetubes I`I and r I2 are arranged to be operatedaaslimiter tubes. Thecontrolgrid inA tube I I is connected to the junction .between capacitory l.' and: potentiometer 8 through a grid resistor.l |31.. Since anodepotential is fed from the positive=termina1 ofltheiD. C; source to the anode ofi tube E-.throughresistors llltandr I5;` it4 follows that.` apotential drop in. resistor- I 5 will vary. with the phase ofI theloscillationsamplied by tube .5. Resistor Iandcapacitor 3l in combinationservel asa high impedance to the-flowqof AJC. energy through the Vl1? C. source. The "oscillations in .thev output circuit-ofi tube laare; therefore, applied to the control grid .in tube/,I I When Vthis tube. is not-v biased to cut off, it is arranged to be conductive and to have a grid-cathode voltage which is slightly positive. The4 output from tube II is, therefore, one of which is substantially of squarewaveiformaton.. l v

The circuit 5off; tube.; It includes, aathedaref. sistorf I-Conneting thecathode .110.1er011nd-1 0.9.- erating potential is'lappliedftothe anode from-the` D. C.- source `through anoderesistorfIQ. l It was; StatedabOV-th tf.y dShareftubed2 wellV as .discharge tube; I I areoperated as 'limiter tubes. That is to say, when either of these tubes: is., rendered conductive.; itY becomes fully Cpuductive, i.- e.. its.grdfcathodef'voltage isslientlr 110.51: tive Theacpntrolrotentials applied tethfgrids these tubes Cnr-the negative,pertsmffxthegcycle.-, According1y..tubel2is arransedftabe .controlled potential l,drop in; the. erdlrsstor I 8i is..r rnentary.z to,that ingthe anodefresistors 9.- and,k varies withithefcharge-on capacitor.l I T hcontrol grid in tube@ I2 isy connected. through. a. ree@V slstor2,0 tothe .junction betweenvcapacitor I'I andresistoml, v

The, cathode Online, l2'. is-,direcuy grandes] Its, anode is. connected to theDQSitive ,terminal0);Y the D.- C. source through a; resistor- 2 I-.Q Y The terg-` minal .l of resistor: 2l adj acont., the .-anodeinzfllbe I2 is also connected to one terminal of a coupling capacitor 22. The other terminal of capacitor 22 is connected to the cathode 24 in one section of a twin diode tube 23 and also the anode 25 in the other section of this tube. The anode 26 in the left hand section of tube 23 is connected to ground through the winding of the tuning fork driving coil 2. The cathode 2'I in the right hand section of tube 23 is directly grounded The amplifier tube IIJ is used to deliver output energy of substantially pure sine wave characteristic to a utilization device. The cathodeof tube I is connected t'o ground through a cathode resistor 28. This resistor is shuntedV by a capacitor 29. The output circuit of Atube I Il includes the primary winding of a transformer 30, this winding being connected to the positive terminal of the D. C. source. The secondary winding of transformer 30 delivers th-e output to any desired utilization device.

VIn' the Voperation of our invention, it will be observed that the limiting action of tubes II and I2`is such'that the'output potentials delivered across" the capacitor 22 are sharply defined. When the anode current of Vtube I2 isl cut ofi', capacitor 22 charges to ther value of the D. C. source through resistor 2| and the space path betweenelectrodes 25 and 21 in the diode rectifier tube; VThe time constant of this circuit is adjusted to be short as compared with the period of tuning fork I. This is necessary in order to insure that even inthe steady state, capacitor 22 shall vcharge fully to +B potential while tube I2 is non-conductive.

When tube I2 is conductive, capacitor 22 dischargesY through the parallel combination of resistor 2IV and thespace path of tube I2 in series with the space path between electrodes 24 and 26 of the rectifier tube 23 and the drive coil 2 of fork `I.' Thus one pulse is supplied to theY drivev coil 2 for each cycle of the fork frequency.

vIt is important to note that the energy in the driving pulse 'applied to the coil 2 is proportional to` the supply voltage derived from,the D. C.' source, the capacity of the capacitor 22, and the ratio Ri-I-Rb where Ri 1s the resistance of resistor 2I, and Rb is the ,resistance of the space path' in tube I2 in the conducting state. ent tubes of the same type at zero biashave been found to be relatively small. These variations are, therefore, eiectively rendered negligible if the value of R1 is chosen to be several times that 0f Rb. f

The Dl C. operating potential applied to the tube rI2 has been indicated as being the same as thatrwhich is applied to tube I I. It is not essential, h'owever, that the same voltages should be usedV with respect to these two tubes.

It willbe well understod by those skilled in the art that the t parameters oi the circuit herein shown and described may be adjusted so that the amplitude of the driving potentials applied to the Variations of Rb with differcoil 2 may be set at an optimum value for avoidance of overdrive while maintaining the substantial sine wave characteristic of output energy i from'the pick-up coil 3. 'I'h'e sine wave shape Vof the output is maintained in the ampliiier tube 5.

Accordingly, a substantially pure sine Wavel is delivered through the potentiometer tap 9 t0 the input circuit of tubeV I0. However, a portion of the output from tube 5 is also utilized in Supplywithout departing from the spirit and scope of the invention itself. Y

We claim:

1. In a low frequency oscillation generator wherein the frequency is controlled by a mechanical Vibrator, a system of electron discharge devices including an ampliiier stage, twoV limiter stages and a full Wave rectifier stage, magnetic driving and pickup Vmeans associated with said vibrator, the input circuit of said amplifier stage being subjectto controlby potentials induced in said pick-up means, capacitors each intercoupling the output and input circuits of successive stages, resistive impedances in circuit with each said capacitor, one of said capacitors being connected between the anode of the second limiter stage'and certain electrodes of said rectier stage, this particular 'capa'citor'in combination with one of said impedan'ces `forming a time Vconstant circuit the charging'tirne'of which' is limited' to a minor fraction of'a cycle of the oscillations to-be generated, and this capacitor being'arranged to discharge rapidly through a circuit which includes the space path of said second limiter stage, one portion of said rectifier stage,V and said magnetic driving means, and a circuit for feeding unilateral pulses ofthe `other polarity from the rectier means to ground.

2`. The invention as claimed in. claim l and including electroniomeans for Vamplifying a component of output energy derived from said amplifier stage, thereby to obtain useful output energy from'said generator.

3. -In a low'frequency oscillation generator of the type having a mechanical vibrator for controlling the'oscillation frequency, electromagnetic means for exciting said vibrator, electromagnetic means for derivingoutput Vpotentials from said vibrator, a, concatenated chain ofv electron tube stages, the firstV stage having an Ainput circuit under control of said output potentials from the vibrator, Iand 'two ysucceeding stages being characterized 'as limiter stages, la full wave rectifier having its unidirectional paths oppositely faced tol 4receive and to block the half cycles of alternating current potentials derivedfrom the second of said limiter stages, a capacitor connected on one side to the anode of the second said limiters'tage and on the other side to both unidirectional paths ofsaid'rectiler, vsaid capacitor in association with the impedance Vof its discharging circuits constituting means'for limiting the duration ofteach pulse which is applied to said electromagnetic exciting means to 'a fraction of one of said half-cycles, and ground connections for the output `from each of said unidirectional paths, one' of said ground connections being arranged to traverse the winding-of said electromagnetic exciting means.

Llg-'Il'ie invention as claimed in claim 3V and including a` potentiometer in the output circuit of the first of said concatenated tube stages, and means for deriving useful output energy from an adjustable tap on said potentiometer,

5. An'electronic oscillator in combination with a resonator for maintaining constant the frequency of the oscillations generated, said oscillator comprising a pluralityof electron discharge devices :each having input and output electrodes and connections to a. source of direct current for energizing the same, means for deriving periodic pulses from said resonator whereby one of said discharge devices in a first stage is controlled, means coupling the output of the first stage to a second stage and thence to a third stage of said discharge devices, means for so adjusting the transconductance of the discharge devices of the second and third stages that they function as limiters, rectifying means receptive to the output of the third stage for directing the energy pulses of each polarity into a separate path, one of which paths includes a device for exciting said resonator, a capacitorintercoupling said third stage and said rectifying means, said capacitor constituting means for limiting to a fraction of a half cycle the duration of said energy pulses as applied to the excitation of said resonator, and means including an amplifier for deriving useful oscillatory energy of substantially pure sine wave characteristic, the last said means being directly coupled to the output circuit of said first stage.

6. Apparatus for stabilizing th'e amplitude and frequency of vibration of a tuning fork comprising an electronic circuit having an amplifier stage, rst and second limiter stages and a full wave rectier having two unilateral space paths, said stages being concatenated in the order named and said second limiter stage having an anode circuit, a circuit including said rectifier and a capacitor for supplying electro-mechanical excitation to said tuning fork, said capacitor being connected to charge through one unilateral space path of said rectifier and to discharge through the other unilateral space path thereof, and means for limiting the discharge period of said capacitor to a fractional part of a half cycle of the tuning forks oscillation, said means including an impedance in the anode circuit of the second limiter stage.

7. An oscillation generator comprising a reso-Y nant system, a vacuum tube having input and output electrodes and said input electrode subjected to voltages set up by said resonant system, limiting apparatus coupled to the output electrode of said tube and having an output circuit, a condenser, a rectifier coupled to the output circuit of said limiting apparatus and connected to said condenser to charge once during each cycle of the Wave output of said limiting apparatus, and a further rectifier connected to said condenser to discharge said condenser through said resonant system once during each cycle of the wave output of said limiting apparatus, the charging and discharging times of said condenser being so adjusted as to occupy periods which are substantially shorter than a half cycle of the resonant frequency of said resonant system.

8. An oscillation generator comprising a resonant system, a vacuum tube having a pair of its electrodes subjected to voltages set up by said resonant system, limiting apparatus coupled to another pair of electrodes of said tube, a condenser, means including one unidirectional space path in a twin diode discharge tube, said tube being coupled to the output circuit of said limiting apparatus whereby said condenser is fully charged once during each cycle of the wave output of said limiting apparatus, and circuit means including the other unidirectional space path in said diode discharge tube for discharging said condenser through said resonant system once during each cycle of the wave output of said limiting apparatus, the charging and discharging times of said condenser being so adjusted as to occupy periods which are substantially shorter than a half cycle of the resonant frequency of said reso-l nant system.

9. An electromechanical resonant system in combination with a vacuum discharge tube having input and output electrodes, a circuit for subjecting said input electrodes to voltages set up by said resonant system, a limiter coupled to said output electrodes, a condenser, a twin diode rectifier having its cathode of one space path and its anode of the other space path connected to one side of said condenser, a circuit connection from the other side of said condenser to the output side of said limiter, and circuit components whereby said condenser is caused to be fully charged once during each cycle of the wave output from said limiter, and is caused to be discharged through a path which includes an element of said resonant system, the values of said circuit components and of said condenser being so chosen as to effect f charging and discharging times of the condenser which are substantially less than half cycles of the wave set up by said resonant system.

10. The combination according to claim 9 wherein said electromechanical resonant system is constituted as a tuning fork having electromagnetic pick-up and driving coils.

11. For use in supplying pulse excitation t0 a tuning fork, an electronic circuit having an amplifier stage, two limiter stages, each said stage having electrode elements, a capacitor and a full wave rectifier having two space paths each provided with a cathode and an anode electrode, said stages being concatenated and said capacitor being connected between the output circuit of the second limiter stage and unlike electrodes of the two space paths in said rectifier, means providing electromechanical pick-up of energy from said tuning fork for applying controlling voltage to said amplifier stage, a discharge circuit connected to said condenser and including electromechanical means for applying energy to said tuning fork, the space path of the second limiter stage and one of said space paths of said rectifier and a power supply system connected throughl impedances to the electrode elements of said stages, said impedances being of predetermined values such that excitation pulses in response to said controlling voltage applied through said one space path of said rectifier to said tuning fork are limited in amplitude by the energy stored in said capacitor, and in duration by the impedance of said discharge circuit.

EUGENE R. SHENK. ALFRED KAI-IN.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,144,236 Whitaker Jan. 17, 1939 2,157,799 Norrman May 9, 1939 2,300,271 Whitaker Oct. 27, 1942 

